It has become increasingly common to store photographically reduced printed information (alpha-numeric and/or graphic) on microfilm in order to achieve a great reduction in the amount of space taken up by the printed information. The microfilm is typically generated according to one of three basic formats, commonly known as "microforms." These are: roll film, cards and microfiche.
Microfilm in the roll format is typically 16, 35, or 105 millimeters wide and is usually stored on a spool, a cartridge (having a single spool), or a cassette (having two spools). Information may be stored either in the comic mode wherein discrete batches of information contain data lines that are parallel to the length of the roll, or in the cine mode wherein a continuous batch of information contains data lines that run perpendicular to the roll length. The card microform is most commonly used for engineering drawings and includes a piece of microfilm mounted in a rectangular aperture punched in a cardboard card. The most common microform is the microfiche which is a cut piece of microfilm, typically including an eye legible title in addition to the reduced data. The most common microfiche size is 105 by 148 millimeters.
Microfilm requires a reader to produce an enlarged image (real or virtual) of the reduced data for viewing by the user. Broadly, microfilm readers may be classified into four categories: desk readers, lap readers, portable readers, and hand held readers.
Desk readers normally weigh in excess of 20 pounds and are intended to sit somewhat permanently on a desk, table top, or other work surface. Desk readers include a light source typically powered by a 110 volt line, a lens for image enlargement, and a projection screen. The microfilm is inserted within the reader and manipulated into a viewing position by an appropriate film transport mechanism. In the case of a spool or cassette, the mechanism would include spool driving means, typically motor driven. For microfiche the mechanism would include a stage for providing rectilinear motion of the microfiche.
The lap reader is similar in concept to the desk reader but is designed more compactly with a weight in the range of 5-12 pounds so that it may rest either on a work surface or in the user's lap. Some lap readers are provided with mechanical film transport means while others require that the user directly manipulate the film into the desired viewing position.
The portable reader is also similar in concept to the desk reader but is designed as separate components which either unfold from a portable compact package or are packaged as separate units, in both cases requiring that they be set up in the use position. The latter type generally have two major components, one including the lamp, lens and microfilm holder and the other including the screen.
Hand held readers differ from the above-described types in that they are designed to be held in one hand. Such readers typically do not project the image onto a screen, but rather use a magnifying lens to produce a virtual image. A battery powered lamp may be provided, but the simpler readers rely on ambient light for illumination. Due to the size of the hand held readers, the microfilm (normally in the form of a microfiche) protrudes from the reader and is maneuvered by the user in order to view the proper portion of the film.
It is clear that the concept of a hand held reader is extremely attractive since it renders the microfilm data base readily accessible to a large number of users at the same time without requiring the provision of a large work area to maintain a large number of desk readers. Moreover, users may make use of data in environments that are not normally conducive to microfilm usage. For example, service personnel can easily and conveniently carry large amounts of maintenance and repair information into the field with them.
However, certain disadvantages of hand held readers have rendered their use less than wholly satisfactory. One such disadvantage is that hand held readers have been designed for two handed use, with one hand holding the reader and the other hand manipulating the film. A second disadvantage, related to the use of the microfiche, is that the microfiche itself extends beyond the confines of the reader with the user manipulating the film by actually grasping the protruding fiche and manually positioning it. Such direct manipulation of the film, possibly inconvenient in itself, further subjects the film to handling that tends to soil it, possibly ultimately rendering it unfit for use. This problem is aggravated should the user require access to the data in a dirty environment such as a repair site, thus undercutting a major advantage of hand held readers to service personnel.
The desk reader, by providing mechanical manipulation of the film, and enclosure of the film within the confines of the reader, is not subject to these disadvantages, and further provides the viewer with an image projected on a screen. This is thought to be more desirable than a virtual image system since it allows more than one viewer to inspect the data at a given time, and is more natural for the viewer, being more like reading data printed directly on a printed page. However, an optical system for providing a sufficiently intense and well focused image on a screen has tended to be highly impractical in the environment of a hand held reader. The reasons that this should be so are best seen in view of a comparison between the desk reader and the hand held reader. In a desk reader where space is relatively unlimited, and where the source of electrical power is 110 volts from the wall socket, the light source can be made as intense as necessary. If heating is a problem, a fan may be provided. The hand held reader on the other hand is battery powered and very small, thereby making it difficult to provide a suitably intense source of light. There are on the market small, low voltage, incandescent bulbs having a lens integrally fabricated into the lamp envelope to provide a greater concentration of light. However, such "lens end" bulbs have tended to be unsatisfactory since the alignment of the lens relative to the base is insufficiently uniform to provide the maximum usable output within the angular tolerance of the hand held reader optical system.
In the context of a desk reader, focusing is not a problem since there is sufficient room for a mechanical focusing mechanism. Moreover, such a focusing mechanism, once set, is unlikely to be jarred by the user so as to require further setting. The hand held reader on the other hand does not have room for a reliable focusing mechanism, and further, the nature of the hand held reader is such that such a focusing mechanism is likely to be jarred during use.
Thus, while the concept of a hand held microfilm reader is a good one, such readers have tended to lack the desirable features of the desk readers, and the potential advantages have tended to go largely unrealized.